I was spotting at Changi Airport yesterday night with one of my friend. I saw a Singapore Airlines A340 took off but when he was at about 800 to 1000 feet, i saw the rear part of the 4 engines are all glowing red. I am suprised to see this happen but at the same time, i am curios. Are the engines too hot or are there some other reasons?

Maybe this is one factor that lead passengers to think there was fire in the engines in the previous cases?

I doubt the metal around the exhaust area would get hot enough to glow, what it might of been is the exhaust gasses still hot enough to glow at night. Like Big777jet pointed out, one would expect such an event occuring where the cone is exposed but than again I am not familiar with the RR engines.

If you look from behind and in darkness at a jet engine running at full power, in most of them you will be able to see a red hue of burning gases through the rotating turbine vanes. But no external engine part (the exhaust cone, etc.) gets hot enough as to glow in the darkness.